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Northern silky oak

Scientific name

Cardwellia sublimis. Family: Proteaceae

Other names

Oak; bull oak; silky oak

Description

  • Large tree grows to 40m high.
  • Stem grows to 2m diameter.
  • Trunk, usually without buttresses, is normally straight.
  • Bark is slightly flaky to non-descript.
  • Outer blaze is commonly biscuit-brown.

Occurrence

  • Distribution is limited to North Queensland between Mt Spec, near Townsville, and Bloomfield.

Appearance

Colour

  • Heartwood is pale pink to brown.
  • Sapwood is usually almost white.

Grain

  • Texture is moderately coarse and varies.
  • Quarter-sawn timber best shows the decorative grain.

Uses

  • Construction: used extensively, in the past, in North Queensland general house framing, cladding, lining, moulding, joinery (particularly windows) and flooring; now confined more to use in joinery.
  • Decorative: plywood, furniture, outdoor furnishings, joinery, shop and office fittings, turnery, carving, inlay work.
  • Others: used, in the past, for boat building (light), brushware, gunstocks, cooperage, vehicle and coach building.

Properties

  • Density: 560kg/m3 at 12% moisture content; about 1.8m3 of seasoned sawn timber per tonne.
  • Strength groups: S6 unseasoned, SD7 seasoned.
  • Stress grades: F4, F5, F7, F8 (unseasoned); F5, F7, F8, F11 (seasoned) when visually stress-graded according to AS 2082—2000: Timber—Hardwood—Visually stress-graded for structural purposes.
  • Joint groups: J4 unseasoned, JD4 seasoned.
  • Shrinkage to 12% MC: 4.7% (tangential), 1.6% (radial).
  • Unit shrinkage: 0.31% (tangential), 0.13% (radial)—these values apply to timber reconditioned after seasoning.
  • Durability above-ground: Class 4 (life expectancy less than 7 years).
  • Durability in-ground: Class 4 (life expectancy less than 5 years).
  • Lyctine susceptibility: untreated sapwood susceptible to lyctid borer attack.
  • Termite resistance: not resistant.
  • Preservation: sapwood readily impregnates with preservative but the heartwood can’t be adequately treated using currently available commercial processes.
  • Seasoning: satisfactorily dries using conventional air and kiln seasoning.
  • Hardness: soft (rated 5 on a 6-class scale) to indent and work with hand tools.
  • Machining: machines, and turns well, to a smooth surface.
  • Fixing: no difficulty using standard fittings and fastenings.
  • Gluing: satisfactorily bonds using standard procedures.
  • Finishing: readily accepts paint, stain and polish; you may need to fill the open grain before polishing the timber.

Identification features

General characteristics

  • Sapwood: creamy white.
  • Heartwood: pink to pinkish-brown..
  • Texture: coarse and irregular, a broad ray figure (pattern) on quarter-sawn surfaces, straight grain.

Wood structure

  • Growth rings: indistinct.
  • Vessels: large, numerous, solitary or in short tangential hoops between the rays; no tyloses, but occasionally vessels are filled with whitish deposits or red-coloured gum.
  • Parenchyma (soft tissue): abundant, aliform and confluent, including vessels between rays; forming loops, generally, concave outwards; an occasional short tangential apotracheal band.
  • Rays: 2 distinct kinds are (a) broad to very broad, plainly visible without a lens on all surfaces, and (b) fine, indistinct even under hand lens.

Other features

  • Burning splinter test: match-size splinter burns to charcoal.
  • Splinter shape: fine needle-like splinters produced when cutting across the grain are characteristic of this species and can be used to separate northern silky oak from similar species.

Research and resources

  • Boland, DJ, Brooker, MIH, Chippendale, GM, Hall, N, Hyland, BPM, Johnston, RD, Kleinig, DA and Turner, JD 2006, Forest trees of Australia, 5th edn, CSIRO Publishing, Collingwood Australia.
  • Bootle, K 2005, Wood in Australia: Types, properties and uses, 2nd ed., McGraw-Hill, Sydney.